Effect of urea on the fluorescence emission of SP-B_N.

<p>(A) Emission spectra of the protein in 0–7.5 M urea were recorded as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158430#pone.0158430.g003" target="_blank">Fig 3</a>. Spectra depicted are: without urea (control, solid line), with 1 M urea (dashed line), with 7.5 M urea (dotted line) and with 7.5 M urea after dialysis (renatured, solid line). (B) Variation of the fluorescence emission at 350 nm with 0–7.5 M urea. Connecting lines are not fitted. Inset: Comparison of secondary structure (% [θ]²²⁰, red circle, data and fitting from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0158430#pone.0158430.g002" target="_blank">Fig 2B</a>) and tertiary structure (FI₃₅₀N·(FI₃₅₀)^-1·10²), blue symbol, data from Fig 4B being N the native form). N and U are omitted for clarity. (C) Phase diagram analysis of urea-induced equilibrium unfolding of SP-B_N. Solid lines are fits of the data by linear regression: 0–2.5 M urea (r = 0.987), 3–6 M (r = 0.97) and 6.5–7.5 M (r = 0.999). Dotted lines are not fitted. I₁, I₂, I₃ and I₄ are intermediate states in the propeptide urea-induced unfolding. Lines are not fitted. Numbers beside the points are denaturant concentration.